1. Field of the Invention
First, this invention relates to a method of compressing picture information. Second, this invention relates to an apparatus for compressing picture information. Third, this invention relates to a method of expanding picture information. Fourth, this invention relates to an apparatus for expanding picture information. Fifth, this invention relates to a method of recording picture information. Sixth, this invention relates to an apparatus for recording picture information. Seventh, this invention relates to a method of reproducing picture information. Eighth, this invention relates to an apparatus for reproducing picture information. Ninth, this invention relates to a recording medium.
2. Description of Related Art
Generally, digital VTR's (video tape recorders) have analog-to-digital converters for changing analog component video signals (analog Y, Cr, and Cb signals) of a given television system such as an NTSC system or a PAL system into corresponding digital component video signals (digital Y, Cr, and Cb signals). Here, the Y signals mean luminance signals. In addition, the Cr signals mean R-Y signals (first color difference signals) while the Cb signals mean B-Y signals (second color difference signals). Specifically, the analog-to-digital converters sample the analog Y, Cr, and Cb signals at given sampling frequencies respectively, and then digitize the samples of the analog Y, Cr, and Cb signals.
In a typical home-use digital VTR, the ratio among the sampling frequencies for the respective analog Y, Cr, and Cb signals is "4:1:1" or "4:2:0 (4:0:2)". The analog Y, Cr, and Cb signals result from interlaced scanning so that two successive fields represented by the analog Y, Cr, and Cb signals compose one frame. ITU-R Recommendation 601 prescribes the following frame sizes. In the case of a 525/60 system (that is, an NTSC system), the frame size is chosen so that the number of samples (pixels) of a Y signal will be equal to 720 (in the horizontal direction) by 480 (in the vertical direction) while the number of samples of each of a Cr signal and a Cb signal will be equal to 180 (in the horizontal direction) by 480 (in the vertical direction). Here, "525" means the number of horizontal scanning lines per frame, and "60" means the number of fields per second. In the case of a 625/50 system (that is, a PAL system), the frame size is chosen so that the number of samples (pixels) of a Y signal will be equal to 720 (in the horizontal direction) by 576 (the vertical direction) while the number of samples of each of a Cr signal and a Cb signal will be equal to 360 (the horizontal direction) by 288 (the vertical direction). Here, "625" means the number of horizontal scanning lines per frame, and "50" means the number of fields per second.
In the case of a 525/60 system, the ratio among the sampling frequencies for the respective analog Y, Cr, and Cb signals is denoted by "4:1:1". According to a 625/50 system, the Cr signal and the Cb signal are transmitted in a line sequence, and hence lines devoid of Cr information and lines devoid of Cb information alternate. Thus, lines related to a sampling frequency ratio of "4:2:0" alternate with lines related to a sampling frequency ratio of "4:0:2". Here, in the case of the 625/50 system, the ratio among the sampling frequencies for the respective analog Y, Cr, and Cb signals is denoted by "4:2:0" for convenience.
In a typical professional-use digital VTR (a typical business-use digital VTR), the ratio among the sampling frequencies for the respective analog Y, Cr, and Cb signals is "4:2:2". Parts of the professional-use digital VTR are more expensive than parts of the home-use digital VTR. It is difficult for the home-use digital VTR to handle digital Y, Cr, and Cb signals related to a sampling frequency ratio of "4:2:2". It is difficult for the professional-use digital VTR to handle digital Y, Cr, and Cb signals related to a sampling frequency ratio of "4:1:1" or "4:2:0".